Basically, there were several serious issues with bzr-hg that didn't really make it fit for release. Rather than keeping it in (in a broken state) and exposing our users to it, I decided to ask for it to be removed for the time being. Once it is more production-ready, it can be added again.

I'm sorry if this affects you. As a workaround, you can also use hg-fastexport and bzr-fastimport to convert Mercurial repositories to Bazaar.